Failed due to PMAX partition as shown above:

ARROW:(MDINH@hawklas):PRIMARY> alter table t_part set interval(numtodsinterval(1,'year'));
alter table t_part set interval(numtodsinterval(1,'year'))
*
ERROR at line 1:
ORA-14759: SET INTERVAL is not legal on this table.

Wrong syntax:

ARROW:(MDINH@hawklas):PRIMARY> alter table t_part set interval(numtodsinterval(1,'year'));
alter table t_part set interval(numtodsinterval(1,'year'))
*
ERROR at line 1:
ORA-14752: Interval expression is not a constant of the correct type